Saboten no Himitsu Manga by Nana Haruta

Saboten no Himitsu is about a girl named Miku who has secretly been in love with a person who never notices anything unless it smacks him in the face! This dumb guy is called Fujioka by his peers. Whenever she tries to confess, he doesn't believe her or else he changes the mood of the conversation! Miku has done everything to get herself noticed by him, even change her appearance completely! But according to him, she's just a cactus alien! But it seems there's more to Fujioka than what meets everyone's eye...